Electric counting device



July 1942. J. ALNAES I 2,291,198

ELECTRIC COUNTING DEVICE Filed March 6, 1939 \T\ gm 23 M Q 22 S f 2 2/ g I ]1Z- E... Z 11 2 Sheets-Shet 2 Patented July 28, 1942 2,291,198 ELECTRIC COUNTING DEVICE Ingvald Julius Alnaes, Osio, Norway, assignor to I. Alnaes A/S, Oslo, Norway, a corporation of Norway, and Ingeniorforretningen Atlas A] S,

Oslo, Norway, a' corporation of Norway Application March 6, 1939, Serial No. 260,152

In Norway February 11, 1938 I 1, Claim.

The present invention relates to electric counting devices for the counting of the revolutions of a shaft; in which device the counting is effected by means of electric impulses, the number of which corresponds to the number of revolutions of the shaft. The device is particularly, but not exclusively, with ship logs.

In accordance with the invention, an electric coil which is fed with an alternating current and is provided with a core of ferromagnetic material is arranged in connection with the shaft, the revolutions of which are to be counted,

circuit of the counting device that the coil constitutes one branch of a Wheatstone bridge which is in balance when the magnetic resistance of adapted for use in connection the magnetic resistance (reluctance) of the said I core being varied in time to the revolutions, in

order to vary the inductive resistance of the coil and thereby give rise to electric impulses which may be counted.

According to one feature of the invention the core is made inthe form of a horse shoe the free ends of which are shaped according to cylindrical surfaces, and the variations of the magnetic resistance of the core is efiected by periodically short circuiting the core by means of a member of magnetically conductive material, the said member rotating, with the shaft and having a cross section in the form of a segment of a circle with the same axis as the cylindrical surfaces of the core ends.

According to a further feature of the invention the variation of the inductance of the coil is effected by moving the core relatively to the the coil core has a maximum.

In the accompanying drawings some embodiments of the invention are illustrated schematically. Figure 1 shows the circuit arrangement of the counting device. The Figures 2 to 6 show the parts of the device which are in direct connection withthe shaft, the revolutions of which are to be counted. Figure 2 is a vertical section through an embodimentand Figure 3 a horizontal section through the device on the line III-III in Figure 2.

Figure 4 is a vertical section on the line IV-IV in Figure 5, through a further embodiment wherein the core is made with straight legs.

Figure 5 is a horizontal section through the same device on the line V-V in Figure 4.

Figure 6 shows one embodiment wherein the core legs are formed according to an arc of a circle, the figure showing a section through the axis of one leg of the core.

In Figure 1, l is the coil, the inductance of which is to be varied in time to the revolutions to be counted and which constitutes one branch in the Whe'atstone'bridge. The opposite branch.

of the said bridge is constituted by a coil 2, the inductance of which is constant and equal to the inductance of coil I when the core of the same has its maximum magnetic resistance. A

"constant alternating voltage is applied to the coil in time to the revolutions of the shaft, the

revolutions of which are to be counted. The core hereby suitably is moved into and out of the central cavity of the coil and, if desired, through the same, the core being of horse shoe form with parallel legs which may be straight or formed according to an arc of a circle. In the first case, the movement of the core is in the direction of the length of the legs, and in the latter case as an oscillation about an axis in the centre of the arc of the circle according to which the legs are formed. Where the core is to be moved in a fluid, which for instance is the case when the counter is to be used in connection with ship logs, the coil conveniently is placed fluidt.ghtly in a housing in such a manner that the central cavity of the coil is in free communication with the fluid. In such cases the core conveniently is surrounded by a sleeve or layer preventing the fluid from penetrating to the core or in between the laminations or wires of the core and giving rise to corrosion.

bridge through the transformer 3 across the terminals 4. In the diagonal of the bridge a counting instrument 5 is inserted in series with rectifiers 6 and I.

The counting instrument 5 may be any con ventional device actuated by the current pulsa tions to register the number thereof. Such an instrument might well ,be of the type shown in the patent to F. C. Harris, No. 1,459,730, patented'June 26, 1923. By variation of the inductance of the coil I, the bridge is brought out of balance The coiisuitably may be so arranged in the and a current impulse will flow through the instrument which,.in a manner known per se, is arranged for the counting of current impulses.

.As the inductance of the coil l varies between a maximum and a minimum value in time to the revolutions of the shaft, the instrument 5 will indicate a number corresponding to the revolutions of the shaft and which for instance by ship logs is a measure of the distance which the ship has travelled.

In the Figures 2 and 3 the coil I is arranged on one leg of a horse shoe core Bof ferromagnetic material, for instance laminated sheet iron. 9 designates the short circuiting member which rotates with the shaft and is so arranged as to periodically short circuit the air gap between the legs of the core 8. The short circuit member 9 is made of magnetically conductive material and is arranged on a circular disc H) which, by means of gears H (only shown in part) are driven from.

the shaft l2. tion of the magnetic resistance of the core 8,

by the sea water flowing through the logythe housing I3 is by means of a wall 15 divided into two rooms, of which the room containing the coil l is filled with insulation material. In order to prevent the generation of eddy currents in the wall 15, the same is provided with a slot l6 extending between the legs of the core 8.

In the Figures 4 and 5, l designates the coils of which one may be arranged on each leg of the horse shoe core 8. As shown in Figure 6, only one coil I may be used, this coil then being placed on one leg of the core. The coils are embedded in insulation material i1 and located in a housing l3 of non-magnetic material, using fluidtight packings i8 and protecting sleeves IS, the inner cavity 20 of each coil being coaxial with an opening in the housing l3. The core 8 operates in cavity 20. By means of couplings and gears (not shown), the core 8 is so connected to the shaft l2 the revolutions of which are to be counted, that the core is moved into and out of the coils l, timed corresponding to the number of revolutions of the shaft. In order to support the coils In order to obtain a'smoo'th variaagainst electromagnetic forces and against possible fluid pressure in the space in which the core is moved, the protecting sleeves l9 surrounding the coils are made of rigid material and are held by means of a yoke 2| secured to the housing by means of bolts 22. A spherical segment pressure member 23 is arranged between the sleeve I9 and the yoke 2|. The core 8 is surrounded by a fluid tight insulation 24.

What I claim is:

A device for counting the revolutions of a rotating shait especially for use in connection with ship logs, comprising in combination, a movable magnetically conductive member adapted to be moved through successively recurring cycles by the shaft the revolutions of which are to be counted, two systems of windings constituting respectively two adjacent branches of a Wheatstone bridge circuit, the reactance of one of the wind in'gs being variable, a transformer having a split secondary the parts of which constitute the two quency for supplying the primary of said transu former, and a series arrangement comprising a rectifier, an impulse counter, and a second rectifier connected in series in the order mentioned, and constituting together the diagonal of the Wheatstone bridge arranged between the transformer secondary junction and the junction of the two winding systems, the variable one of the said two systems of windings being so positioned in relation to the said movable magnetically conductive member that the inductive reactance of the same is varied in time to the movements of said member, the two systems of windings being so dimensioned relatively to each other that the bridge is in a state of balance when the inductive 

